Bipyridine Units Research Articles

Evaluation and Elucidation of DNA‐Containing Viologen Dendrimer Complex Formation

During the galley proof corrections of the original article the wrong version of Figure was inadvertently provided. The formula on the left must have two nitrogen atoms to depict the correct redox state of a doubly substituted viologen. The correct Figure is given below. (Figure presented.) Schematic depiction of the reduction of 4,4′-bipyridinium units to the radical cations, and the derived cyclic voltammogramms. The Authors.

2,2'-Bipyridin-1'-ium 1-oxide bromide monohydrate.

The title compound 2,2'-bipyridin-1'-ium 1-oxide bromide crystallizes as a monohydrate, C10H9N2+·Br-·H2O. Structural disorder is observed due to the fact that protonation, as well as oxidation, of the N atoms of 2,2'-bi-pyridine occurs at either of the N atoms. The disorder extends to the remainder of the cation, with a refined occupancy rate of 0.717 (4) for the major moiety. An intra-molecular N-H⋯O hydrogen bond forces the bi-pyridine unit into an s-cis conformation. Each pair of neighbouring 2,2'-bipyridin-1'-ium ions forms a dimeric aggregate by hydrogen bonds between their respective N-O and the N-H functions. These dimers and hydrogen-bonding inter-actions with bromide ions and the water mol-ecule give rise to a complex supra-molecular arrangement.

Selective Coassembly of Aromatic Amino Acids to Fabricate Hydrogels with Light Irradiation-Induced Emission for Fluorescent Imprint.

Controlling the structural parameters in coassembly is crucial for the fabrication of multicomponent functional materials. Here a proof-of-concept study is presented to reveal the α-substituent effect of aromatic amino acids on their selective coassembly with bipyridine binders. With the assistance of X-ray scattering technique, it is found that individual packing in the solid state as well as bulky effect brought by α-substitution determines the occurrence of coassembly. A well-performed hydrogels based on the complexation between certain aromatic amino acids and bipyridine units are successfully constructed, providing unprecedented smart materials with light irradiation-triggered luminescence. Such hydrogels without the phase separation and photobleaching during light irradiation are able to behave fluorescent imprint materials. This study provides a suitable protocol in rationally designing amino acid residues of short peptides for fabricating self-assembled multicomponent materials. In addition, this protocol is useful in screening potential functional materials on account of diverse self-assembly behavior.

Fine-Tuning LUMO Energy Levels of Conjugated Polymers Containing a B←N Unit

The LUMO and HOMO energy levels (ELUMO/EHOMO) are key parameters for conjugated polymers, which can greatly affect their applications in organic opto-electronic devices. In this manuscript, with donor–acceptor (D–A) type conjugated polymers based on double B←N bridged bipyridine (BNBP) unit, we report fine-tuning of ELUMO of conjugated polymers in a wide range via substitutions on both D unit and A unit. We synthesize eight D–A type conjugated polymers with alternating electron-deficient BNBP unit and electron-rich bithiophene (BT) unit in the main chain. By changing the substitutes on BNBP or BT, the ELUMO of these polymers can be finely tuned in a wide range from −3.3 eV to −3.7 eV. We comprehensively investigate the electronic structures, photophysical properties, charge-transporting properties and polymer solar cell (PSC) device applications of these polymers. In PSC devices, these BNBP-based polymers can be used either as electron donors (with high-lying ELUMO/EHOMO) or as electron acceptors (with lo...

Immobilization of luminescent Platinum(II) complexes on periodic mesoporous organosilica and their water reduction photocatalysis

Pt(II) complexes have been immobilized on a periodic mesoporous organosilica (PMO) consisting of 2,2′-bipyridine (bpy) units bridged by siloxane bonds (BPy-PMO). Although these Pt(II) complexes are luminescent in their discrete molecular states, the luminescence properties of the immobilized complexes largely depend on the origin of the emission; luminescence is quenched when the emission originates from the 3ππ* excited state of bipyridine due to the coupling of the CH bending vibration of the bpy and the Si-O stretching vibration of the siloxane framework, while luminescence is maintained when the 3ππ* excited state of bipyridine is not the lowest excited state. Although the simple coexistence of Pt(0) nanoparticles and Pt(II) complexes did not catalyze water reduction even in the presence of an electron relay, photocatalytic water reduction is observed when Pt(0)/Pt(II)-co-immobilized BPy-PMOs are used. This result clearly demonstrates the importance of the integration of photosensitizers and catalysts on the PMO for enhancing intermolecular electron-transfer processes.

Mechanical-Bond-Protected, Air-Stable Radicals.

Radical templation centered around a heterotrisradical tricationic inclusion complex DB•+⊂DAPQT2(•+), assembled from an equimolar mixture of a disubstituted 4,4'-bipyridinium radical cation (DB•+) and an asymmetric cyclophane bisradical dication (DAPQT2(•+)), affords a symmetric [2]catenane (SC·7PF6) and an asymmetric [2]catenane (AC·7PF6) on reaction of the 1:1 complex with diazapyrene and bipyridine, respectively. Both these highly charged [2]catenanes have been isolated as air-stable monoradicals and characterized by EPR spectroscopy. X-ray crystallography suggests that the unpaired electrons are delocalized in each case across two inner 4,4'-bipyridinium (BIPY2+) units forming a mixed-valence (BIPY2)•3+ state inside both [2]catenanes, an observation which is in good agreement with spin-density calculations using density functional theory. Electrochemical studies indicate that by replacing the BIPY2+ units in homo[2]catenane HC•7+-composed of two mechanically interlocked cyclobis(paraquat-p-phenylene) rings-with "zero", one, and two more highly conjugated diazapyrenium dication (DAP2+) units, respectively, a consecutive series of five, six, and seven redox states can be accessed in the resulting SC·7PF6 (0, 4+, 6+, 7+, and 8+), HC·7PF6 (0, 2+, 4+, 6+, 7+, and 8+), and AC·7PF6 (0, 1+, 2+, 4+, 6+, 7+, and 8+), respectively. These unique [2]catenanes present a promising prototype for the fabrication of high-density data memories.

Reversible end-to-end assembly and disassembly of gold nanorods based on pH-responsive host-guest interaction

The reversible end-to-end assembly and disassembly of gold nanorods (GNRs) were efficiently realized by utilizing the pH-responsive host-guest interaction. The guest compound, containing a 4,4'-bipyridine unit and a disulfide group, was synthesized, and could form the 2:1 inclusion compounds with cucurbit[8]uril (CB[8]) host molecules quickly in aqueous solution. Due to the fact that the inclusion compounds could be destroyed and re-formed by adjusting the solution pH, the terminal-modified GNRs could realize the reversible end-to-end assembly and disassembly. The end-to-end assembly and disassembly of GNRs were well characterized by UV–Vis spectra and TEM images. This method, employing supramolecular host-guest interaction to control the reversible linear assembly and disassembly of GNRs, may provide a new idea for the design of smart organic-inorganic hybrid materials.

Long-Lived Polypyridyl Based Mononuclear Ruthenium Complexes: Synthesis, Structure, and Azo Dye Decomposition.

Two mononuclear ruthenium complexes [(bpy)2RuIIL1/L2](ClO4)2 ([1]2+/[2]2+) (bpy-2,2' bipyridine, L1 = 2,3-di(pyridin-2-yl)pyrazino[2,3-f][1,10]phenanthroline) and L2 = 2,3-di(thiophen-2-yl)pyrazino[2,3-f][1,10]phenanthroline have been synthesized. The complexes have been characterized using various analytical techniques. The complex [1]2+ has further been characterized by its single crystal X-ray structure suggesting ruthenium is coordinating through the N donors of phenanthroline end. Theoretical investigation suggests that the HOMOs of both complexes are composed of pyridine and pyrazine unit of ligands L1 and L2 whereas the LUMOs are formed by the contribution of bipyridine units. The low energy bands at ∼480 nm of the complexes can be assigned as MLCT with partial contribution from ligand transitions, whereas the rest are ligand centered. The complexes have shown RuII/RuIII oxidation couples at E1/2 at 1.26 (70 mV) V and 1.28 (62 mV) V for [1]2+ and [2]2+ vs Ag/AgCl, respectively, suggesting no significant role of distal thiophene or pyridine units of the ligands. The complexes are emissive and display solvent dependent emission properties. Both complexes have shown highest emission quantum yield and lifetime in DMSO (ϕ = 0.05 and τavg = 460 ns and λmaxem at 620 nm for [1]2+; ϕ = 0.043 and τavg = 425 ns and λmaxem at 635 nm for [2]2+). Further, the long luminescent lifetime of these complexes has been utilized to generate reactive oxygen species for efficient azo dye decomposition.

Direct synthesis of Fe(III) immobilized Zr‐based metal–organic framework for aerobic oxidation reaction

A Zr‐based metal–organic framework with bipyridine units (UiO‐67) has been utilized for the immobilization of catalytically active iron species via a post‐synthetic metalation method. UiO‐67 bipyridine MOF was synthesized through a simple solvothermal method and was shown to have a UiO‐type structure. Post‐synthetic metalation of UiO‐67 MOF was performed for the immobilization of the catalytically active FeCl3. FT‐IR and EDX element map suggested that FeCl3 is coordinately bonded to the UiO‐67 bipyridine framework. The synthesized UiO‐67‐FeCl3 catalyst was used for the aerobic oxidation of alcohols and benzylic compounds in the presence of molecular oxygen. In addition, the UiO‐67‐FeCl3 catalyst can be reused as a solid heterogeneous catalyst without compromising its activity and selectivity.

A Boat-Shaped Tetracationic Macrocycle with a Semiconducting Organic Framework.

We report the synthesis of a tetracationic macrocycle which contains two N,N'-bis(methylene)naphthalenediimide units inserted in between the pyridinium rings of the bipyridinium units in cyclobis(paraquat-p-phenylene) (CBPQT4+ or "blue box") and describe the investigation of its potential use in materials for organic electronics. The incorporation of the two naphthalenediimide (NDI) units into the constitution of CBPQT4+ , not only changes the supramolecular properties of the tetracation in the solid state, but also has a profound influence on the electrochemical and electronic behavior of the resulting tetracationic macrocycle. In particular, the solid-state (super)structure, investigated by single-crystal X-ray diffraction, reveals the formation of a three-dimensional (3D) supramolecular framework with ca. 2.8 nm diameter one-dimensional (1D) hexagonal channels. Electrochemical studies on solid-state thin films of the macrocycle show that they exhibit semiconducting properties with a redox-conductivity of up to 7.6×10-4 S m-1 . Moreover, EPR and ENDOR spectroscopies show that charge is equally shared between the NDIs within the one-electron reduced state of the NDI-based macrocycle on the time scale of these techniques.

A Boat‐Shaped Tetracationic Macrocycle with a Semiconducting Organic Framework

AbstractWe report the synthesis of a tetracationic macrocycle which contains two N,N′‐bis(methylene)naphthalenediimide units inserted in between the pyridinium rings of the bipyridinium units in cyclobis(paraquat‐p‐phenylene) (CBPQT4+ or “blue box”) and describe the investigation of its potential use in materials for organic electronics. The incorporation of the two naphthalenediimide (NDI) units into the constitution of CBPQT4+, not only changes the supramolecular properties of the tetracation in the solid state, but also has a profound influence on the electrochemical and electronic behavior of the resulting tetracationic macrocycle. In particular, the solid‐state (super)structure, investigated by single‐crystal X‐ray diffraction, reveals the formation of a three‐dimensional (3D) supramolecular framework with ca. 2.8 nm diameter one‐dimensional (1D) hexagonal channels. Electrochemical studies on solid‐state thin films of the macrocycle show that they exhibit semiconducting properties with a redox‐conductivity of up to 7.6×10−4 S m−1. Moreover, EPR and ENDOR spectroscopies show that charge is equally shared between the NDIs within the one‐electron reduced state of the NDI‐based macrocycle on the time scale of these techniques.

Polymer Electron Acceptors with Conjugated Side Chains for Improved Photovoltaic Performance

The development of polymer electron acceptors lags far behind that of polymer electron donors. A general approach to improve photovoltaic performance of polymer electron donors is to incorporate conjugated side chains to the electron-rich unit. In this article, we introduce the “conjugated side chain” strategy to molecular design of polymer electron acceptors by incorporating conjugated side chains to the electron-deficient unit. The polymer backbones consist of alternating electron-deficient double B←N bridged bipyridine (BNBP) unit and electron-rich thiophene or selenophene unit. Polymer electron acceptors are developed by incorporating conjugated alkoxyphenyl side chains to the BNBP unit. Compared with conventional alkyl side chains, the conjugated alkoxyphenyl side chains endow the polymer electron acceptors with low-lying LUMO energy levels, enhanced π–π stacking, and high electron mobilities, which are very desirable for electron acceptors. The resulting all-PSCs exhibit an enhanced power conversion...

Hierarchical Growth of Supramolecular Structures Driven by Pimerization of Tetrahedrally Arranged Bipyridinium Units.

A shape-persistent molecule, featuring four bipyridinium units, has been synthesized that upon reduction undergoes intermolecular pimerization because of the rigid architecture of the molecule. The pimerization process has been investigated by a variety of techniques, such as absorption measurements, EPR spectroscopy, as well as gamma and pulse radiolysis, and compared with the behavior of a model compound. Computational studies have also been performed to support the experimental data. The most interesting feature of the tetramer is that pimerization occurs only above a threshold concentration of monoreduced species, on the contrary to the model compound. Furthermore, there is an increase of the apparent pimerization constant by increasing the concentration of reduced bipyridinium units. These results have been interpreted by the fact that pimerization is favored in the tetrahedrally shaped molecule because of a cooperative mechanism. Each multiply reduced molecule can indeed undergo multiple intermolecular interactions that enhance the stabilization of the system, also leading to hierarchical supramolecular growth. The resulting supramolecular system formed by such intermolecular pimerization should exhibit a diamond-like structure, as suggested by a simplified modeling approach. The intermolecular nature of the pimerization process occurring in the tetramer has been demonstrated by measuring the corresponding bimolecular rate constant by pulsed radiolysis experiments.

Synthesis and unusual response to potassium of bipyridinium-benzocrown ether conjugate

A bipyridinium derivative appending a benzocrown ether, in which the phenyl unit in the benzocrown ether was directly bounded to the N-position of the bipyridinium unit, has been synthesized. The compound showed a yellow color associated with an intramolecular charge transfer (CT), which was affected by the presence of alkali and alkaline earth metal ions. An unusual CT response to K+ for 1 was observed and could be applicable for K+ sensing.

Synthesis of Dimethyl-Substituted Polyviologen and Control of Charge Transport in Electrodes for High-Resolution Electrochromic Displays

Electrochromic (EC) polymers such as polyviologens have been attracting considerable attention as wet-processable electrodes for EC displays, thanks to their brilliant color change accompanied with reversible redox reactions. To establish wider usage, achieving multicolor and high-resolution characteristics is indispensable. In this paper, we demonstrated that the introduction of substituents such as methyl groups into bipyridine units changed the stereostructure of the cation radicals, and thus shifted the color (e.g., ordinary purple to blue). Also, by relaxing excessive π-stacking between the viologen moieties, the response rate was improved by a factor of more than 10. The controlled charge transport throughout the polyviologen layer gave rise to the fabrication of EC displays which are potentially suitable for the thin film transistor (TFT) substrate as the counter electrodes with submillimeter pixels. The findings can be versatilely used for the new design of polyviologens with enhanced electrochemical properties and high-resolution, multicolor EC displays.

2,2'-Bipyridyl-Embedded Cycloparaphenylenes as a General Strategy To Investigate Nanohoop-Based Coordination Complexes.

Because of their unique cyclic architectures, tunable electronic properties, and supramolecular chemistries, cycloparaphenylenes (CPPs) have the potential to act as a new class of ligands for coordination cages, metal-organic frameworks, and small-molecule transition-metal complexes. However, currently there is no general strategy to coordinate the cyclic framework to a variety of metal centers. We report here a general and scalable synthetic strategy to embed 2,2'-bipyridine units into the backbone of CPPs. We use this approach to synthesize a 2,2'-bipyridine-embedded [8]CPP, which we show can successfully coordinate to both Pd(II) and Ru(II) metal centers. The resulting coordination complexes, a Pd(II)-nanohoop dimer and a bis(bipyridyl)ruthenium(II)-functionalized nanohoop, show unique solid-state and photophysical properties. This work provides a proof of concept for a general strategy to use nanohoops and their derivatives as a new class of ligands.

Three-Legged 2,2'-Bipyridine Monomer at the Air/Water Interface: Monolayer Structure and Reactions with Ni(II) Ions from the Subphase.

The behavior of compound 2 [1,3,5-tri(2,2'-bipyridin-5-yl)benzene] with three bipyridine units arranged in a star geometry is investigated in the presence and absence of Ni(ClO4)2. Its properties at the air-water interface as well as after transfer onto a solid substrate are studied by several techniques including Brewster angle microscopy, X-ray reflectivity, neutron reflectivity, X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and atomic force microscopy combined with optical microscopy. It is found that compound 2 within the monolayers formed stays almost vertical at the interface and that at high Ni2+/2 (Ni2+/2 = 4000, 20'000) ratios two of the three bipyridine units of 2 are complexed, resulting in supramolecular sheets that are likely composed of arrays of linear metal-organic complexation polymers.

Spectroelectrochemistry of alternating ambipolar copolymers of 4,4′- and 2,2′-bipyridine isomers and quaterthiophene

First report of π-conjugated push-pull copolymer systems with 4,4′-bipyridine moieties in the main macromolecular chain is presented. C-substitution pattern of electropolymerisable bithiophene pendants at the 4,4′-bipyridine unit offered the versatility to retain the latter as free amine, or convert it into bipyridylium salt. Both structures have been prepared and investigated, delivering the first example of a polymer with viologen unit making up the extended π-bond. Detailed electrochemical, spectroelectrochemical and quantum chemical study of these new polymer systems and their 2,2′-bipyridine analogues has shown that while linear structure and extended conjugation in the latter help it to accommodate charge carriers characteristic for heavily doped polythiophene, the conjugation break afforded by the meta substitution pattern across the 4,4′-pirydyl unit makes the polymer behave like an ensemble of shorter oligomeric segments with better defined electron transitions and sharper, and faster electrochromic response. Effective π-π interchain coupling between α,ω-bis(2-pyridyl)quaterthiophene repeating units was observed, whereas intramolecular interactions were found to dominate in the linear 2,2′-bipyridyl based polymer. While the bithiophene derivative of methyl viologen electropolymerised less easily than its corresponding non-quaternised derivative, the resulting polymer films demonstrated decent stability when subject to subsequent p- and n-doping, featuring pronounced charge trapping/detrapping signatures. Furthermore, ion pairing between the viologen and weakly basic PF6− and CF3SO3− counterions has been found to impact the redox chemistry of bithiophene functionalised viologen structure. Experimental findings have been confronted with results of quantum chemical computations helping to elucidate the electrochemical and spectroelectrochemical observations made. Presented study delivers insights into the doping processes taking place in conjugation disrupted 4,4'-bipyridine core copolymers, helping to evaluate their potential as substrates for new tuneable π-conjugated polymeric systems.

Chiral Nitroxide/Copper‐Catalyzed Aerobic Oxidation of Alcohols: Atroposelective Oxidative Desymmetrization

AbstractA series of chiral imidazolidinone‐based hydroxylamines were evaluated as catalysts for the aerobic oxidation of alcohols in the presence of CuIOTf/bpy/NMI as co‐catalysts. In such conditions, the in situ produced nitroxides catalyze the oxidation of benzylic alcohols. When the imidazolidinone ring is substituted by a copper‐coordinating heterocycle, the outcome of the oxidation is clearly improved in terms of rate and maximal conversion. Enantiopure catalysts featuring a bipyridine unit covalently attached in close vicinity to the hydroxylamine could be readily prepared and used in the enantioselective aerobic oxidation of three model axially‐prochiral diols. These results demonstrate for the first time the validity of a O2/chiral nitroxide/copper combination for enantioselective oxidations.

Synthesis and photoelectric properties of new Pr-bonded polymers by coordination of isopropyloxide and bipyridine unit

A series of novel praseodymium (Pr)-bonded polymers were successfully synthesized via the coordination reaction and palladium-catalyzed Suzuki coupling reaction of 2,7-dibromo-9,9′-dioctylfluorene and different amounts of 5,5′-dibromo-2,2′-bipyridine. The resulting polymers were characterized by 1H-NMR and GPC. The photoluminescence (PL) and electroluminescence (EL) properties of the resulting polymers were studied to explore the effects of the Pr triisopropyloxide. The results showed that the incorporation of Pr into the polymers caused better coplanarity and effective intermolecular or intramolecular interaction, leading to the higher emission intensity at long-wavelength. Further, it was also found that the emission light color could be tuned from blue to green by introduction of a small amount of Pr into the polymer main chain. A single-layer green emitting EL device based on PF(BipyPr)6 with 6 mol% Pr content was fabricated. The device had a low turn-on voltage of 6 V, a brightness of 705.3 cd·m−2, the maximum luminous efficiency of 1.53 cd·A−1 and the maximum power efficiency of 0.69 lm·W−1.